1. Field of the Invention
The following invention relates generally to instruments for cutting bone during surgery. More particularly, the instant invention is directed toward surgical saw blades adapted to be operatively coupled to powered surgical instruments.
2. Description of the Prior Art
Powered oscillating surgical saws with coupled bone cutting surgical saw blades are widely used in orthopedic surgery. Surgeons have long faced the problem of reaching narrow and deep recesses with power-driven surgical saw blades. During surgery, the protection of soft tissue such as tendons, ligaments, muscles, vascular and neurological structures is crucial. As such, various power transmission mechanisms, which transmit power from the proximally (near the surgeon or user) disposed powered oscillating surgical saw to the distal (far end) cutting edge of the surgical saw blade, have been designed to limit the midline oscillatory excursion of the distal cutting edge, i.e., limit the cutting action of the distal cutting edge, thereby reducing the exposure of adjacent soft tissue structures to the high-speed oscillatory excursion of the surgical saw blade.
Such known power transmission mechanisms can include translation mechanisms, for example, the translation mechanisms described in U.S. Pat. Nos. 1,179,910, 2,854,981 and 7,497,860. Translation mechanisms typically include moving internal parts which transmit motion from an attached powered oscillating surgical saw to a distal pivoting cutting edge. For example, as shown in FIG. 1A, a known surgical saw blade assembly 110 may include a plurality of linked gears 113. A connected powered oscillating surgical saw can rotate the proximal most gear 113a in a small arc 115. The resulting motion is transmitted through the plurality of linked gears 113, causing distal cutting member 116 to oscillate about a distally disposed center of oscillation or pivot point 118 and moving the distal toothed cutting edge 117 in a small arc 119. The pivot radius 122 of the distal cutting member 116 extends from the distally disposed center of oscillation 118 to the distal tips of the teeth of distal toothed cutting edge 117. Another example is shown in FIG. 1B, which shows a known surgical saw blade assembly 160 which comprises a pair of push rods 163a and 163b. To move the distal cutting edge 169 in a small arc 171, the first push rod 163a is driven in one direction, for example, as indicated by arrow 165a, while the second push rod 163b is driven in the opposite direction, for example, as indicated by arrow 165b. This reciprocating action of the push rods 163a, 163b causes the distal toothed cutting member 167 to oscillate about a distally disposed center of oscillation or pivot point 168. The pivot radius 172 of the distal toothed cutting member extends from the distally disposed center of oscillation 168 to the distal tips of the cutting edge 169.
These translation mechanisms are not without their disadvantages. With every additional moving component within a translation mechanism, there typically needs to be adequate dimensional clearance provided between the moving internal parts to allow them to move. By providing for such required freedom of motion, efficiency can be lost in such translation mechanisms. Furthermore, surgical saw blades typically operate at about 10,000 cycles per minute. Thus, much friction between the moving internal parts can be created when the surgical saw blade is in use. As such, efficiency can further be lost between the power source and the cutting edge of the surgical saw blade with a translation mechanism.
Additionally, these translation mechanisms often require their cutting edges to pivot from a distally disposed pivot point, for example pivot points 118 and 168 as shown in FIGS. 1A and 1B, respectively. As a result, the teeth of the cutting edges engage bone at a very sharp and unstable angle. This sharp, unstable engagement angle can cause the surgical saw blade to buck and “kick”, i.e., become caught upon the bone being cut by the point of a tooth. This tendency of the surgical saw blade to buck and “kick” will typically reduce the overall cutting efficiency and accuracy of the saw blade assembly. The instability of the surgical saw blade can also translate back to the surgeon's hand, increasing the risk of an inaccurate bone cut. In at least some cases, the surgeon may be able to rein in the instability by maintaining a tighter grip on the proximally disposed powered oscillating surgical saw. However, maintaining a tighter grip increases the fatigue of the surgeon and the instability can manifest itself as torsional stresses placed upon the moving parts of the saw blade assembly.
In the specific cases of translation mechanisms incorporating reciprocating push rods, for example, the translation mechanisms shown in FIG. 1B and those described in U.S. Pat. Nos. 2,854,981 and 7,497,860, such torsional stresses may cause binding of the long push rods against the stationary components of the saw blade assembly. With the saw blade assembly operating at high speeds, for example, approximately 10,000 to 14,000 cycles per minute, such binding can cause additional friction between the push rods and the stationary elements of the saw blade assembly. This additional friction creates heat and can cause the moving portions of the saw blade assembly to slow down, further reducing the cutting efficiency of the cutting edge. If such binding starts to occur, a surgeon may mistake the resulting increased resistance as cutting resistance from the bone and push harder on the saw blade. Pushing harder on the saw blade assembly increases the very undesirable possibility of the saw blade skiving upwardly, which causes an inaccurate bone cut. Worse yet, the saw blade may dive deeper into the bone, well beyond the intended bone resection level.
Thus, known bone cutting surgical saw blades incorporating such translation mechanisms may not be ideal for efficiently and stably engaging and cutting bone at high speeds. Due to their multitude of moving internal parts, they can be mechanically inefficient. These known surgical saw blades can further be hampered by increased frictional forces caused by torsional stresses placed upon the saw blade assembly.
Other surgical saw blades without complicated translation mechanisms are also well known. These saw blades are described, for example, in co-assigned U.S. Pat. Nos. 6,022,353, 6,503,253, 6,723,101, and 7,527,628, the entire contents of which are incorporated by reference herein. Such saw blades are well-accepted in the orthopedic industry as having optimal bone cutting operational efficiency and simplicity in their unitary construction. However, these saw blades leave room for improvement in their ability to protect adjacent soft tissue from exposure to the cutting action of the blades.
As such, there is a need for improved surgical saw blades which engage and cut bone in a smooth, stable, and efficient manner, while protecting the adjacent soft tissue from exposure to the cutting action of the saw blade.
Other references of interest may also include: U.S. Publication Nos. 2009/0093815 and 2009/0093814, the Applications of which are co-assigned and fully incorporated herein by reference; U.S. Publication Nos. 2008/0243125 and 2008/0027449; and U.S. Pat. Nos. 5,839,196, 5,439,472, 5,382,249, 4,768,504, 4,617,930, and 1,726,241. U.S. Design patent Ser. No. 29/335,690, the contents of which are fully incorporated herein by reference, may also be of interest.